Effects of temperature gradient in Mboundi field

[Audio] RESERVOIR GEOLOGY - GEOLOGY FOR ENERGY RESOURCES Introduction C. Tarchiani – Eni SpA Natural Resources - Reval - ARMS December 2024.

[Audio] Reservoir basic definition Reservoir: Volume of rock with sufficient porosity and permeability to allow, in the presence of appropriate geological conditions, the accumulation of hydrocarbons in commercially exploitable quantities It defines the reservoir, an accumulation of hydrocarbons in a porous rock It can be produced by a well because the rock is permeable The well creates a depletion causing the release of fluids from the pores The fluid produced are replaced by a displacing fluid (water or gas).

[Audio] Eni's field in the World … Eni is involved in Production of more 170 assets in 26 countries and Exploring in 16 countries Deep Offshore Arctic Plant Nikaitchuq - Alaska Abo deep offshore - Nigeria Exploration Exploration & Production Desert Offshore Brass terminal - Nigeria BRN treatment plant - Algeria Zatchi field - Congo Swamp.

[Audio] Reservoir study and reservoir management The exploitation of a hydrocarbon field is a "way of operating" in a given fiscal and contractual scenario optimizing the production of hydrocarbons. Optimizing hydrocarbon production means to maximize their recovery during the life of the field. This objective is achieved in two ways 1) Reservoir studies 2) Proper operational management (Reservoir Management) 4.

[Audio] Reservoir study and reservoir management Optimizing hydrocarbon production means to maximize their recovery during the life of the field. This objective is achieved in two ways: 1) Reservoir studies 2) Proper operational management (Reservoir Management) What is a reservoir study for? 1. Investigate and model the reservoir (Reservoir Model) 1. geological aspects (structural, stratigraphic, sedimentological), 2. properties of the rocks that constitute it (Rock Properties), 3. properties of the fluids contained in them (Fluid Properties) and their mutual interactions 2. Identify the natural drive mechanisms of the reservoir 3. Calculate hydrocarbons in place (OHIP - Volumetrics) 4. Estimate Recoverable Reserves and predict production performance (at the scale of individual wells and the field) 5. Select the best development and production scenario for the field 6. Investigate all possible options to improve hydrocarbon recovery (EOR / IOR) 5.

[Audio] Reservoir study and reservoir management Deliverables of a reservoir study Volume of Original Hydrocarbons in place (OHIP) Reservoir 3D model Well target and location Production profiles (for recoverable reserves) Risk analysis Reservoir monitoring and management strategy.

• Volume of Original Hydrocarbons in place (OHIP) • Reservoir 3D model • Well target and location • Production profiles (for recoverable reserves) • Risk analysis • Reservoir monitoring and management strategy Deliverables of a reservoir study Reservoir study and reservoir management.

[Audio] Volume of Original Hydrocarbon in Place (OHIP) OHIP estimated volume of HC in known reservoirs prior to any production activity. RESERVES the amount of HC discovered in a field that can be produced with the available technology (related to a defined development scenario). RECOVERY FACTOR = RESERVES/OHIP 8.

[Audio] Volume of Original Hydrocarbon in Place (OHIP) GBV = Gross Bulk Volume (total volume of the reservoir rock) N/G = Net over Gross Ratio (ratio from the volume of the hydrocarbon bearing intervals and the total volume of the reservoir rock) PHI = Porosity (calculated from the Net intervals) Sw = Water Saturation (calculated from the Net intervals) FVF = Formation Volume Factor, Bo for oil and Bg for gas (factor referred to the volume of the hydrocarbon at standard condition) GBV * N/G * PHI * (1- Sw) OHIP = ----------------------------------FVF.

[Audio] Original Hydrocarbon volume Field classification (by API) Classes OIL field GAS field MSTB BSm3 SUPER GIANT > 5000 > 850 GIANT 500 - 5000 85 - 850 MAJOR 100 - 500 17 - 85 Class A 50 - 100 8,5 - 17 Class B 25 - 50 4,2 - 8,5 Class C 10 - 25 1,7 - 4,2 Class D 1 - 10 0,17 - 1,7 Class E < 1 < 0,17.

[Audio] Reservoir study and reservoir management Deliverables of a reservoir study Volume of Original Hydrocarbons in place (OHIP) Reservoir 3D model Well target and location Production profiles (for recoverable reserves) Risk analysis Reservoir monitoring and management strategy.

[Audio] Reservoir 3D Model From a basic english dictionary: Model: A small object, usually built to scale, that represents in detail another, often larger, object From a technical english dictionary: Model: A description of observed behaviour, simplified by ignoring certain details. Models allow complex systems to be understood and their behaviour predicted, but may give incorrect descriptions and predictions 12.

[Audio] Reservoir 3D Model Delta river Geostatistical model 13.

[Audio] Modelling the reality Geostatistical model.

[Audio] Modelling the reality 15. 15 Modelling the reality.

[Audio] Modelling the reality Process-oriented modelling.

[Audio] eni's Geomodeling Workflow eni's suite of geomodeling tools INTERPRET2 OFM PVTi GAP GEOLOG TECHLOG PROSPER TECHLOG PETREL Engineering Data Petrophysical Interpretation Characterization Reservoir Definition & Characterization TECHLOG RECALL etc, Data Collection, PETREL QC & Analysis RMS SKUA 3D Reservoir Geometry & Property Modeling Reservoir Seismic Interpretations Other Studies Sedimentological Model Shared-earth modeling software is eni' standard practice to 3D geological modeling.

[Audio] Reservoir study and reservoir management Deliverables of a reservoir study Volume of Original Hydrocarbons in place (OHIP) Reservoir 3D model Well target and location Production profiles (for recoverable reserves) Risk analysis Reservoir monitoring and management strategy.

[Audio] Well Target & Location Reservoir Fluid-Flow Simulation Model.

[Audio] Reservoir study and reservoir management Deliverables of a reservoir study Volume of Original Hydrocarbons in place (OHIP) Reservoir 3D model Well target and location Production profiles (for recoverable reserves) Risk analysis Reservoir monitoring and management strategy.

[Audio] Production Profiles Flow prediction from a reservoir as a function of the number of wells 21.

[Audio] Eni Long term production profile Mozambique (Cyprus) Angola Nigeria Ghana Indonesia USA Ghana Angola Australia Norvay DO NOTHING 22.

[Audio] Reservoir study and reservoir management Deliverables of a reservoir study Volume of Original Hydrocarbons in place (OHIP) Reservoir 3D model Well target and location Production profiles (for recoverable reserves) Risk analysis Reservoir monitoring and management strategy.

[Audio] Reservoir Monitoring and Management Strategy The different salinity of the water produced in different wells indicates different mixing percentages between formation water and injection water in wells 7, 9 and 11 22 20 18 16 14 RE - INJECTION START - UP ( 3/8/84 ) 12 + WATER SALINITY ( Na CI ) , g/lt 10 8 J J A S O 6 L E G E N D : WELL 1 WELL 7 WELL 9 WELL 11 INJECTOR A + 24.

[Audio] Reservoir study and reservoir management Optimizing hydrocarbon production means to maximize their recovery during the life of the field. This objective is achieved in two ways: 1) Reservoir studies What does Reservoir Management consist of? 2) Proper operational management (Reservoir Management) 1. Define, apply and possibly update the production strategies proposed by the reservoir study 2. Define, apply and update reservoir monitoring strategies through appropriate data acquisitions (continuous, sporadic, special) 3. Evaluate the production performance of the field by identifying any possible improvements 4. Decide and plan specific interventions on wells (Well Interventions and Workovers), evaluating the results 5. Keep the reservoir model updated based on real production data and monitoring results 25.

[Audio] Multidisciplinary approach to reservoir study One of the most relevant problem of a reservoir study is to properly integrate all the available information into a consistent model. The key point becomes the understanding of the global objective of the study, while all the disciplines involved in the study must define sub-objective which are strongly dependent upon the global ones An integrated study is a challenging task to perform. The reservoir is a very complex object in itself, which must be characterised from a variety of viewpoints, with a large number of parameters and with a remarkable degree of accuracy. It is mostly indirect: The only direct access to the reservoir are the cores It is based on a small support volume: except from seismic and well testing all the available data are relevant to small or very small support volume. It is varied: Information comes from different sources (cores, seismic, surface data, borehole data) 26.

[Audio] Multidisciplinary approach to reservoir study Information comes from different sources (cores, seismic, surface data, borehole data) A typical example is Porosity Sources: Cores -> direct measurement on very small volume Logs -> indirect measurement on a volume bigger than core but negligible respect to the reservoir volume Seismic -> the whole volume is sampled but the vertical resolution is normally very poor 27.

[Audio] Multidisciplinary approach to reservoir study A balance between complexity and accuracy Increasing the level of complexity of a particular work does not necessarily ensure improved accuracy in overall results Improved accuracy does not automatically guarantee compliance with the objective of the study. It is better to avoid introducing excessive details that only increase the complexity of the study "Fit for purpose" "Keep it simple" 28.

[Audio] Multidisciplinary approach to reservoir study FIELD LIFE Discovery Well Production start-up EXPLORATION Decommisioning DEVELOPMENT Opportuni Opportuni ties ties PRODUCTION/OPERATION Drill & Postdrill Pre-drill Explorat GE1 GE2 GE3 GE4 Generatio Evaluatio Evaluati ion n n on Appraisal Commissioning, Hand-over to Decommissio Running Prospect Evaluation ning Start Up and Performance GP2 First Period Production GP1 Study Production & Improvement Test & Ending Production Check Hand Over Accep tance Package Preliminary Integrated Reservoir HC in HC free Study Evaluation Integrated Reservoir Integrated Reservoir Study Study Concept Selection Integrated Reservoir Study First Period Production Running Production & Improvements E&P Management System 29.

[Audio] Multidisciplinary approach to reservoir study Professional skills Geophysicist Gechemestry Operation Geologist EXPLORATION Structural Geologist Sedimentologist Petrophysicist DEVELOPMENT / PRODUCTION Reservoir Geologist Reservoir Engineer 30.

[Audio] Multidisciplinary approach to reservoir study Reservoir Geologist Evaluation of the development potential of Oil&Gas discoveries, well location and evaluation/determination of the relevant requirements in terms of acquisition of well data and linked procedures. Construction of integrated 3D "geocellular" models taking into account all the geoscientific data (petrophysical, geological, sedimentological, acoustic, etc.) available. Participation in research projects and technological innovation in the field of study of oil and gas deposits. Specialist support for project teams and the various geographical units. Preparation and supervision of geological work on the study of deposits including reservoir geometry, well correlation, integrated petrophysical characterization, modelling of facies and petrophysical parameters, evaluation of the volumes of hydrocarbons in place. Identification of the key uncertainties in the sub-surface data and in the resulting interpretation processes and analysis of the possible alternatives and risk scenarios (Risk Analysis). 31.

[Audio] Multidisciplinary approach to reservoir study Petroleum Engineering (Reservoir) Area Overview Mission Target ➢Evaluate the Hydrocarbon Volume in ➢Perform integrated reservoir studies, assuring Place. the up-to-date technical approach. ➢Define possible Development Schemes ➢Promote and execute R&D projects. and associated Reserves. ➢Know-How development on static & dynamic ➢Select the Optimum Development reservoir modelling & subsidence. ➢Best practices definition and diffusion; best Scheme to maximise the Recovery Factor and project NPV (flow rate and capex). use of reservoir software ➢Establish procedures for a correct ➢Provide specialistic support to Business Unit Reservoir Management. and Project Teams ➢Professional Area Management: international posting, recruiting, training and education.

[Audio] Reservoir Engineering Role ( 1 / 2 ) understanding of the interaction between the porous medium and fluids present Study of hydrocarbon displacement mechanism Simulation of reservoir model(s) representative of geology, fluid & rocks properties, wells, production, etc. Evaluation of the amount of recoverable hydrocarbons study of methods for increasing oil recovery.

[Audio] Reservoir Engineering Role (2/2) Study of development scenarios of a field Number, location and production regime of wells Production forecasts Monitoring and analysis of the production performance of the well to improve the exploitation of the reservoir Calculation of oil and gas reserves Periodic estimate for producing fields Evaluation of any acquisition / disposal of reservoirs.

[Audio] RESERVOIR CLASSIFICATION: www.eni.it. www.eni.it RESERVOIR CLASSIFICATION :.

[Audio] Reservoir an accumulation (TRAP) of hydrocarbons in a porous rock CHARACTERISTICS: It can be produced because the rock is permeable The well creates a depletion causing the release of fluids from the pores (FLUIDS COMPOSTION) The fluid produced are replaced by a displacing fluid (water or gas).

[Audio] TRAPS - STRUCTURAL 37. TRAPS - STRUCTURAL 37.

[Audio] TRAPS - STRATIGRAPHIC Pinch out Isolated sand bars or channel 38.

[Audio] Types of reservoir Elements that define the Reservoir type : Characteristics of the rock Clastic Reservoir Carbonate Reservoir Fractured Reservoir Fluids composition Gas Condensate gas Oil Location "on-shore" "off-shore" "deep-water".

[Audio] ROCK CHARACTERISTICS The traditional distinction between clasts reservoir, fractured carbonate and reflects a substantial difference in the porosity and permeability of these reservoir rocks..

[Audio] ROCK CHARACTERISTICS - CLASTIC RESERVOIR Clastic Reservoir A reservoir composed of rocks made up of fragments of pre-existing rocks or minerals that were transported some distance from their place of origin, deposited, compacted and cemented. Sandstone and shale are the most common and prevalent clastics. Handbook of Oil Industry Terms & Phrases, R.D. Langenkamp The petrophysical properties are strongly correlated with the original textural characteristics of the reservoir rock (i.e. the environment of deposition and associated geological processes). Some diagenetic phenomena can have a major impact in the modification of the original features: Cementation illite o chamosite formation.

[Audio] ROCK CHARACTERISTICS - CARBONATE RESERVOIR Carbonate Reservoir A reservoir composed of limestone and/or dolomite. Geology of Carbonate Reservoirs, M.A. Wayne In carbonate reservoir petrophysical properties are the combined effect of several geological processes. Therefore, it's important to identify and reconstruct the sequence of events (burial history, diagenesis) resultingin the petrophysical properties observed..

[Audio] ROCK CHARACTERISTICS - CARBONATE RESERVOIR - DIAGENESIS Post depositional processes (mechanical / geochemical) can deeply change the porosity leading to: Reduction of the porosity for compaction, plastic deformation, cementation, growth of mineral Authigenic creation of secondary porosity by dissolution, fracturing, and reduction in volume as a result of dolomitization Vuggy porosity carbonate (core sample) Vuggy, karstic porosity in El Abra reef limestone (Mexico). Scholle & Patsoules AAPG European Region Energy Conference, Athens Nov 2007 43 Figures and tables from P.Glover.

[Audio] ROCK CHARACTERISTICS - FRACTURED RESERVOIR Natural Fractured Reservoir A reservoir in which naturally occurring fractures either have or are predicted to have a significant effect on reservoir fluid flow. Geologic Analysis of Naturally Fractured Reservoirs, R.A. Nelson Fractures are elements universally present in rocky bodies. From this point of view, each reservoir could be fractured. Fractures in limestone, Bristol Channel (Belayneh, 2003) What is important is not the presence of fractures but the role of these components during the production of a reservoir..

[Audio] ROCK CHARACTERISTICS - FRACTURED RESERVOIR Schematic Distribution of Fractured Reservoir Types All 100 % k f Fractures I II III % of Total Permeability Decreasing Effect of Matrix IV Increasing Effect of Fractures M All Nelson (1999) 100% k m Matrix % of Total Porosity 100% f m 100% f f Type I : Fractures provide the essential storage capacity and permeability. Type II : Fractures provide the essential reservoir permeability. Type III : Fractures assist permeability in an already producible reservoir. Type IV : Fractures provide no additional porosity or permeability but create significant reservoir anisotropy (barriers)..

[Audio] FLUIDS COMPOSITION - Phase Diagram PVT characteristics The reservoir fluids are constituted by complex mixtures of hydrocarbons: their composition can vary from dry gas, heavy oils, bitumen. The property depends on: Composition PT reservoir condition The behavior of state of reservoir fluids is described by a phase diagram, which summarizes his behavior PVT (pressure, volume, temperature). The PVT characteristics constitute the basic elements for the simulation of volumetric behavior of reservoir fluids and should be an integral part also of the geological model construction. 46.

[Audio] FLUIDS COMPOSITION - Phase Diagram Bubble point curve: locus of minimum P, T values at GAS- CONDENSATE UNDERSATURATED RESERVOIRS OIL RESERVOIRS which only the existence of liquid phase is possible SINGLE PHASE GAS RESERVOIRS Dew point curve: locus of maximum values P, T at which only the existence of the gas phase is CRICONDENBAR possible Critical Point (Tc, Pc): connects the Bubble and Dew Point lines; at this point the properties of the two phases are identical Cricondentherm: Tmax (beyond the critical point) at which coexistence of two phases is still possible Cricondenbar: Pmax (above the critical point) at which coexistence of two phases is still possible 47.

[Audio] FLUIDS COMPOSITION - CLASSIFICATION OF FLUIDS Dry Gas Cond Gas Light Oil Gas secco Gas a cond. Ret Olio Volatile Black Oil Component % molare % molare % molare % molare N2 6.25 0.29 0.12 0.16 CO2 2.34 1.72 1.5 0.91 C1 81.13 79.14 69.59 36.47 C2 7.24 7.48 5.31 9.67 C3 2.35 3.29 4.22 6.95 IC4 0.22 0.51 0.85 1.44 NC4 0.35 1.25 1.76 3.93 IC5 0.09 0.36 0.67 1.44 NC5 0.03 0.55 1.12 1.41 C6 0 0.61 1.22 4.33 C7+ 0 4.8 16.64 33.29 Nitrogen Carbon Dioxide Methane Ethane Propane i-Buthane n-Buthane i-Penthane n-Penthane Hexane Heptane + The temperature depends on the depth of the reservoir The phase diagram depends on the composition of the fluid.

[Audio] FLUIDS COMPOSITION - PHASE DIAGRAM Phase diagram and reservoir fluids Black Oil: the fluid at reservoir conditions is undersaturated. With the production, and the consequent decrease of pressure (isothermal depletion) you will reach the bubble point with the consequent liberation of gas Volatile Oil: the fluid in reservoir conditions is undersaturated, but the amount of liberated gas is much greater compared to a black oil, because of the greater presence of light hydrocarbons in the mixture Condensed gas: in this case Tc <Tres, but the coexistence region of the two phases (Cricondentherm) extends to the right of the Tc; therefore, the reduction of pressure due to the crossing of the line of the dew point, results in condensation of liquid from the originally gaseous mixture Dry gas: Tc <Tres; during the depletion isotherm Tres is always higher than the cricondentherm and are not formed in the liquid reservoir; the separation conditions are outside of the two-phase region, and therefore there is not even the formation of liquid hydrocarbons to the surface. These gas mixtures are composed of very light hydrocarbons (mainly methane and ethane) Wet gas: the situation is very similar to that of a dry gas, in the sense that it has no formation of liquid in the reservoir; However, the PT of the separator conditions counts in the two-phase region, and then there is the formation of liquid hydrocarbons on the surface 50.

[Audio] FLUIDS COMPOSITION - PHASE DIAGRAM Phase Envelopes for different Reservoir Fluids 35 T res, Pres 30 Tc>Tr Volatile Oil Tc<TR 25 Gas Condensate 20 Black Oil 15 Pressure (MPa) Tc>Tr Gas 10 5 0 -50 0 50 100 150 200 250 300 350 400 Temperature (°C).